Method and apparatus related to on-board message repeating for vehicle consist communications system

ABSTRACT

A communications method for a vehicle consist ( 10 ) comprising a lead vehicle ( 14 ) having a first ( 29 A) and second ( 29 B) antenna associated with a respective first ( 28 A) and second ( 28 B) transceiver and a remote vehicle ( 12 A/ 12 B/ 12 C) having a third ( 29 A) and fourth ( 29 B) antenna associated with a respective third ( 28 A) and fourth ( 28 B) transceiver. The method further comprises transmitting an outbound message from the first transceiver ( 28 A) via the first antenna ( 29 A) or from the second transceiver ( 28 B) via the second antenna ( 29 B), the outbound message comprising a plurality of message bytes, receiving the outbound message at the third ( 29 A) and fourth ( 29 B) antennas and associated third ( 28 A) and fourth ( 28 B) transceivers, determining correct bytes and error bytes in the outbound message as received at the third transceiver ( 28 A), determining correct bytes and error bytes in the outbound message as received at the fourth transceiver ( 28 B), and assembling a reconstructed message using correct bytes from the message received at the third transceiver ( 28 A) and the fourth transceiver ( 28 B).

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority to and is a continuation-in-partof patent application filed on Mar. 23, 2005 and assigned applicationSer. No. 11/088,090 (now U.S. Pat. No. ______), which claims the benefitof the U.S. Provisional Patent Application No. 60/565,591 filed on Apr.26, 2004.

BACKGROUND OF THE INVENTION

Distributed power railroad train operation supplies motive power andbraking action from a lead locomotive (or lead unit) and one or moreremote locomotives (or remote units) spaced apart from the lead unit ina train. In one configuration, a distributed power train comprises alead locomotive at a head end of the train, a remote locomotive at anend of train (EOT) position and one or more mid-train locomotivesdisposed between the head end and the end of train. Distributed trainoperation may be preferable for long train consists to improve trainhandling and performance, and especially for trains operating overmountainous terrain.

In a distributed power train, each lead and remote locomotive suppliesmotive power and braking action for the train. Motive and brakingcommand messages are issued by an operator in the lead locomotive andsupplied to the remote locomotives over a radio frequency communicationssystem, (such as the prior art LOCOTROL® distributed powercommunications system, available from the General Electric Company ofSchenectady, N.Y.) comprising a radio frequency link (channel) andreceiving and transmitting equipment at the lead and the remote units.The receiving remote locomotives respond to these commands to applytractive effort or braking effort to the train, and advise the lead unitof the receipt and execution of the command. The lead unit also sendsother messages to the remote units, including status request messages.The remote units respond by sending a status reply message back to thelead unit.

In a train having two or more directly coupled remote locomotives, thecoupled locomotives function in unison via control signals transmittedover their connected MU (multiple unit) lines. One of the locomotives isdesignated as a controlling remote unit with respect to the distributedpower communications system. Only the controlling remote unit isconfigured to receive commands transmitted by the lead unit and respondto the lead unit with appropriate reply messages.

One of the most critical aspects of train operation is the predictableand successful operation of the air brake system. The air brake systemcomprises locomotive brakes in each locomotive (including the leadlocomotive and all the remote locomotives) and car brakes at eachrailcar. The lead unit locomotive brakes are controlled by thelocomotive operator in response to a position of a locomotive brakehandle, and the rail car brakes are controlled in response to a positionof an automatic brake handle. The locomotive brakes can also becontrolled by the automatic brake handle.

The automatic brake handle or controller controls a pressure in a fluidcarrying brake pipe that extends the length of the train and is in fluidcommunication with a car brake system for applying or releasing carbrakes at each railcar in response to a pressure change in the brakepipe. Specifically, a control valve (typically comprising a plurality ofvalves and interconnecting piping) at each railcar responds to changesin the brake pipe fluid pressure by applying the brakes (in response toa decrease in the brake pipe fluid pressure) or by releasing the brakes(in response to an increase in the brake pipe fluid pressure). The fluidwithin the brake pipe conventionally comprises pressurized air. Operatorcontrol of the automatic brake handle in the lead locomotive initiates apressure drop at the lead unit that propagates along the brake pipe tothe end of the train. The control valve at each railcar senses thepressure drop and in response thereto supplies pressurized air from alocal railcar reservoir to wheel brake cylinders that in turn draw brakeshoes against railcar wheels. The railcar reservoir is recharged by airwithdrawn from the brake pipe during non-braking operational intervals.

A brake release is also commanded by the lead operator by controllingthe automatic brake handle to effect a pressure increase in the brakepipe. The pressure increase is sensed at the railcars and in responsethe brake shoes are released from the railcar wheels.

In a distributed power train, in addition to regulating the brake pipepressure to effect application and release of the railcar brakes, thelead unit commands remote unit brake applications and releases bysending an appropriate signal to the remote units via the communicationschannel. As described further below, brake applications and releases arethus more rapidly affected along the length of the train due to theparticipation of both the lead unit and the remote units. With somelimitations as required to maintain train control, in a distributedpower train a brake command or brake release can also be commanded bythe lead or the remote locomotives.

The railcar brakes can be applied in two modes, i.e., a service brakeapplication or an emergency brake application. In a service brakeapplication, braking forces are applied to the railcar to slow or bringthe train to a stop at a forward location along the track. Duringservice brake applications the brake pipe pressure is slowly reduced andthe brakes are applied gradually in response thereto. The operatorcontrols the rate at which the pressure is reduced by operation of theautomatic brake control handle. A penalty brake application is one formof a service brake application in which the brake pipe is reduced tozero pressure, but the evacuation occurs at a predetermined rate, unlikean emergency brake application as described below, and the railcars donot vent the brake pipe during the penalty brake application.

An emergency brake application commands an immediate application of therailcar brakes through an immediate evacuation or venting of the brakepipe at the lead unit (and the remote units of a distributed powertrain). When a railcar senses a predetermined pressure reduction rateindicative of an emergency brake application, the railcar also vents thebrake pipe to accelerate propagation of brake pipe evacuation along thetrain. Unfortunately, because the brake pipe runs for several thousandyards through the train, the emergency brake application does not occurinstantaneously along the entire length of the brake pipe. Thus thebraking forces are not uniformly applied at each railcar to stop thetrain.

On distributed power trains, braking is accomplished by venting thebrake pipe at both the lead and remote locomotives, thus acceleratingthe brake pipe venting and application of the brakes at each railcar,especially for those railcars near the end of the train. As can beappreciated, brake pipe venting at only the lead unit in a conventionaltrain requires propagation of the brake pipe pressure reduction alongthe length of the train, thus slowing brake applications at railcarsdistant from the lead unit. For a distributed power train with anoperative communications link between the lead and remote units, whenthe train operator commands a brake application (e.g., a service or anemergency brake application) by operation of the automatic brake controlhandle at the lead unit, the brake pipe is vented and a brakeapplication command is transmitted to each remote unit over the radiofrequency communications link. In response, each remote unit also ventsthe brake pipe. Thus braking action at the remote locomotives followsthe braking action of the lead unit in response to signals transmittedby the communications system.

A brake release initiated at the lead unit is also communicated over theradio frequency link to the remote units so that the brake pipe isrecharged to a nominal pressure from all locomotives, reducing the brakepipe recharge time.

If an emergency brake application is initiated at the lead locomotive bythe train operator or in response to a detected failure condition, theradio frequency communication system sends an emergency brake signal toeach of the remote locomotives over the radio frequency link. Inresponse, the remote locomotives evacuate the brake pipe. This techniquepermits faster execution of the emergency brake application since thebrake pipe is evacuated from all of the locomotives, rather than fromonly the lead locomotive as in a conventional train.

FIGS. 1 and 2 schematically illustrate an exemplary distributed powertrain 10, traveling in a direction indicated by an arrowhead 11, whereinone or more remote units 12A-12C are controlled from either a lead unit14 (FIG. 1) or a control tower 16 (FIG. 2). A locomotive 15 iscontrolled by the lead unit 14 via an MU line 17 connecting the twounits. The teachings of the present invention can be applied to thedistributed power train 10 and a communications system operativetherewith as described below.

It should be understood that the only difference between the systems ofFIGS. 1 and 2 is that the issuance of commands and messages from thelead unit 14 of FIG. 1 is replaced by the control tower 16 of FIG. 2 andcertain interlocks of the system of FIG. 1 are eliminated. Typically,the control tower 16 communicates with the lead unit 14, which in turnis linked to the remote units 12A-12C.

In one embodiment, a communications channel of the communications systemcomprises a single half-duplex communications channel having a three kHzbandwidth, where the messages and commands comprise a serial binary datastream encoded using frequency shift keying modulation on one of fouravailable carrier frequencies. The various bit positions conveyinformation regarding the type of transmission (e.g., message, command,alarm), the substantive message, command or alarm, the address of thereceiving unit, the address of the sending unit, conventional start andstop bits and error detection/correction bits. The details of themessages and commands provided by the system and the transmission formatof individual messages and commands are discussed in detail in commonlyowned U.S. Pat. No. 4,582,280, which is hereby incorporated byreference.

The distributed power train 10 of FIGS. 1 and 2, further comprises aplurality of railcars 20 interposed between the remote units 12A/12B andbetween the remote unit 12C (of FIG. 1). The arrangement of thelocomotives 14 and 12A-12C and railcars 20 illustrated in FIGS. 1 and 2is merely exemplary, as the present invention can be applied to otherlocomotive/railcar arrangements. The railcars 20 are provided with anair brake system (not shown in FIGS. 1 and 2) that applies the railcarair brakes in response to a pressure drop in a brake pipe 22, andreleases the air brakes upon a pressure rise in the brake pipe 22. Thebrake pipe 22 runs the length of the train for conveying the airpressure changes specified by the individual air brake controls 24 inthe lead unit 14 and the remote units 12A, 12B and 12C.

In certain applications, an off board repeater 26, further describedbelow, is disposed within radio communication distance of the train 10for relaying communications signals between the lead unit 14 and theremote units 12A, 12B and 12C.

The lead unit 14 and the remote units 12A, 12B and 12C are provided withindependent transceivers 28A and 28B operative with respective antennas29A and 29B for receiving and transmitting communications signals overthe communications channel. The off board repeater 26 and the controltower 16 are each provided with the transceiver 28 operative with theantenna 29 for receiving and transmitting communications signals overthe communications channel.

The lead unit transceiver 28 is associated with a lead station 30 forgenerating and issuing commands and messages from the lead unit 14 tothe remote units 12A-12C, and receiving reply messages therefrom.

Commands are generated in the lead station 30 in response to operatorcontrol of the motive power and braking controls within the lead unit14, as described elsewhere herein or automatically as required. Eachremote unit 12A-12C and the off board repeater 26 comprises a remotestation 32 for processing, repeating and/or responding to transmissionsfrom the lead unit 14 and for issuing reply messages and commands. Thelead station 30 and the remote stations 32 are responsive to independentsignals from both the transceivers 28A and 28B.

The four primary types of radio transmissions carried by thecommunications system include: (1) link messages from the lead unit 14to each of the remote units 12A-12C that “link” the lead unit 14 and theremote units 12A-12C, i.e., configure or set-up the communicationssystem for use by the lead unit 14 and the remote units 12A-12C, (2)link reply messages that indicate reception and execution of the linkmessage, (3) commands from the lead unit 14 that control one or morefunctions (e.g., application of motive power or braking) of one or moreremote units 12A-12C and (4) status and alarm messages transmitted bythe one or more remote units 12A-12C that update or provide the leadunit 14 with necessary operating information concerning the one or moreremote units 12A-12C.

Each message and command sent from the lead unit 14 is broadcast to allof the remote units 12A-12C and includes a lead unit identifier for useby the remote units 12A-12C for determining that the sending lead unitis the lead unit of the same train. An affirmative determination causesthe remote unit 12A-12C to execute the received command.

Messages and alarms sent from one of the remote units 12A-12C alsoinclude the sending unit's address. As a result of a previouslycompleted link-up process, the receiving unit, i.e., the lead or anotherremote locomotive, can determine whether it was an intended recipient ofthe received transmission by checking the sending unit's identificationin the message, and can respond accordingly.

These four message types, including the address information included ineach, ensure a secure transmission link that has a low probability ofdisruption from interfering signals within radio transmission distanceof the train 10. The messages allow for control of the remote units12A-12C from the lead unit 14 and provides remote unit operatinginformation to the lead unit 14.

Although most commands are issued by the lead unit 14 and transmitted tothe remote units 12A-12C for execution as described above, there is onesituation where a remote 12A-12C issues commands to the other remoteunits and the lead unit 14. If a remote unit 12A-12C detects a conditionthat warrants an emergency brake application, the remote transmits anemergency brake command to all other units of the train. The commandincludes identification of the lead locomotive of the train and willtherefore be executed at each remote unit, as if the command had beenissued by the lead unit.

Throughout the description of the present invention, the terms “radiolink”, “RF link” and “RF communications” and similar terms describe amethod of communicating between two links in a network. It should beunderstood that the communications link between nodes (locomotives) inthe system in accordance with the present invention is not limited toradio or RF systems or the like and is meant to cover all techniques bywhich messages may be delivered from one node to another or to pluralothers, including without limitation, magnetic systems, acousticsystems, and optical systems. Likewise, the system of the presentinvention is described in connection with an embodiment in which radio(RF) links are used between nodes and in which the various componentsare compatible with such links; however, this description of thepresently preferred embodiment is not intended to limit the invention tothat particular embodiment.

In a distributed power train, responsive to an operator-initiatedcommand, the communications system at the lead unit transmits to eachremote unit a radio frequency (RF) message representing the command.Such commands can include locomotive throttle or traction commands andair brake, dynamic brake and electric brake commands. In the case of anair brake command, upon message receipt, the brake command is executedat each remote unit to accelerate command response at the railcars,since the remote units receive the radio frequency message before theysense the brake pipe pressure change. For example, if the operatorcommands a brake application, the brake pipe is vented at the lead unitand the pressure reduction propagates along the length of the trainuntil reaching the end-of-train car. Depending on train length, severalseconds may elapse before the pressure reduction reaches the lastrailcar. Venting the brake pipe at the lead and remote locomotives, thelatter in response to the RF message, accelerates the brake pipe ventingand application of the brakes at each railcar, especially for therailcars near the end of the train. Thus braking actions at the remotelocomotives follow the braking actions of the lead unit in response tothe RF signals transmitted by the communications system.

A brake release initiated at the lead unit is also communicated over theradio frequency link to the remote units so that the brake pipe isrecharged to its nominal pressure from all locomotives, reducing brakepipe recharge time.

If the train operator initiates an emergency brake application at thelead locomotive, the communication system sends an emergency brakesignal to each of the remote locomotives over the radio frequency link.The remote locomotives evacuate the brake pipe to provide fasterexecution of the emergency brake application since the brake pipe isevacuated from all of the locomotives, rather than from only the leadlocomotive as in a conventional train.

In general, messages sent over the communications system permit theapplication of more even tractive forces to the railcars and improvebraking performance as each locomotive can effect a brake application atthe speed of the RF signal, rather than the slower speed at which thepneumatic brake pipe braking signal propagates along the train.

When the distributed power train is operating in an environment whereeach remote unit is expected to receive command messages sent by thelead unit, for example when the train is traveling along a relativelystraight length of track with no proximate obstructions to a radiofrequency signal, the communications system is operative in a normalmode. In this mode, no communications losses, interruptions or repeatedmessages (because the message did not reach its intended destinationwhen first transmitted) are anticipated. Most messages issued in thenormal mode are controlled according to a fixed priority messageprotocol, according to which each remote unit transmits a status messageresponsive to a lead-issued command message after a predeterminedinterval from transmission of the command. Thus each remote unit isassigned a time slot, measured from transmission of the lead unitcommand message, during which each remote unit transmits its message.

A timing diagram of FIG. 3, where the system is described for a railroadtrain comprising a lead unit and four remote units, illustrates theconcepts associated with the fixed priority message protocol for normalcommunications. The concepts described in conjunction with FIG. 3 can beapplied to a train comprising more or fewer than four remotelocomotives.

According to this scheme, at a time t=650 msec, the lead unit transmitsa command message (for example, a brake command, a traction command, adynamic brake command, etc.) that is expected to be received by allremote locomotives in the distributed power train. As can be seen inFIG. 3, each transceiver (also referred to as a radio) is allocated a 30msec interval to turn on, and an exemplary command message length is 193msec. After a lapse of the predefined interval from the leadtransmission, for example 50 msec as indicated in FIG. 3, a first remotelocomotive retransmits the command message and its status message (forexample, the first remote locomotive is venting the brake pipe inresponse to the brake command). The status message is intended for thelead locomotive so that the train operator is advised of the firstremote unit's response to the command. Also note that each remote unitretransmits the command message with its status message to maximize thelikelihood that the command is received by all remote locomotives. Theturn-on time, message duration, etc. illustrated in FIG. 3 are merelyexemplary and can vary depending on the application and specificationsof the components that comprise the communications system.

The second remote locomotive repeats the command message and transmitsits status message after a predetermined delay, for example 50 msec,from the end of the first remote's transmission. The command repeatingand status transmitting process continues until all remote locomotiveshave repeated the command message and transmitted their respectivestatus message. An end of message condition occurs when the last remotehas transmitted its status, after which the lead unit is free totransmit another command message to the remote locomotives. In the FIG.3 embodiment, the end of message occurs at t=2896 msec or 2271 msecafter the lead unit's initial transmission.

When the lead unit transmits a command message, the lead unit will notknow whether the message was received by all the remote units in thetrain until a remote status message is received from each remote unit(wherein the status messages indicates receipt and execution of thecommand message) or a status message is not received from one or more ofthe remote units (lack of a status message indicates the command messagewas not received). Thus according to one embodiment of thecommunications system, to ensure that each remote unit receives thecommand messages, it is repeated by each remote unit.

Note that it is possible that one or more remote status messages may notbe received by the lead unit. When this is the case, the lead unitretransmits the command message and awaits a reply status message fromeach remote unit in the train. One feature of the present invention, tobe described below, increases the likelihood that all status messagesare received at the lead unit, thus reducing the retransmit probability,without significantly impacting the overall transmission timing for thecommand and status messages.

In addition to the fixed priority protocol described above, certaincommands, e.g., an emergency brake application, are classified as highpriority command messages and are transmitted according to a differentpriority protocol than the fixed priority protocol. Still other commandmessages, e.g., a communications system check, operate according toother priority protocols that control transmission of these commands andthe reply by the remote units.

As the distributed power train passes through certain terraintopographies or track segments with proximate natural or man-madeobstructions, a line-of-sight communications link between the sendingand the receiving units may be interrupted. Thus commands and statusmessages may not be reliably received by the receiving unit, i.e., thelead locomotive for messages sent from a remote unit, and a remotelocomotive for messages sent from the lead unit. Although high-power,robust transceivers may be capable of successfully transmitting thesignal to the receiving unit under certain operating conditions, suchequipment can be relatively expensive. Further, in some operatingscenarios even a high-power transceiver cannot successfully effectcommunications, such as when a long train travels a curved track segmentadjacent a natural obstruction such as a mountain, where thecommunications path between the lead unit and one or more remote unitsis obstructed by the mountain. Also, as the train passes through atunnel certain transceivers may be unable to communicate with othertransceivers aboard the locomotives.

To improve system reliability, one embodiment of the distributed powertrain communications system comprises the off-board repeater 26 (seeFIG. 1) for receiving messages sent from the lead unit 14 and repeating(retransmitting) the message for receiving by the remote units 12A-12C.This embodiment may be practiced along a length of track that passesthrough a tunnel, for example. In such an embodiment the off-boardrepeater 26 comprises an antenna 29 (e.g., leaky coaxial cable mountedalong the tunnel length) and the remote station 32 for receiving andretransmitting lead messages that are received by all the remote units12A-12C within RF communications range of the repeater antenna 29.

BRIEF DESCRIPTION OF THE INVENTION

According to one embodiment, the present invention comprises acommunications method for a vehicle consist comprising a lead poweredvehicle having a first antenna associated with a first transceiver and asecond antenna associated with a second transceiver and a remote poweredvehicle having a third antenna associated with a third transceiver and afourth antenna associated with a fourth transceiver. The method furthercomprises transmitting an outbound message from the first transceivervia the first antenna or from the second transceiver via the secondantenna, the outbound message comprising a plurality of message bytes,receiving the outbound message at the third and the fourth antennas andthe associated third and fourth transceivers, determining correct bytesand error bytes in the outbound message as received at the thirdtransceiver, determining correct bytes and error bytes in the outboundmessage as received at the fourth transceiver, and assembling areconstructed message using correct bytes from one of the messagereceived at the third transceiver and the message received at the fourthtransceiver.

According to another embodiment, the present invention comprises acommunications method for a vehicle consist comprising a lead poweredvehicle and a plurality of remote powered vehicles. The method furthercomprises transmitting an outbound message from the lead poweredvehicle, the outbound message comprising a plurality of message bytes,one or more of the plurality of remote powered vehicles receiving andretransmitting the outbound message, receiving a first occurrence of theoutbound message at a one of the plurality of remote powered vehicles,receiving a second occurrence of the outbound message at the one of theplurality of remote powered vehicles, determining correct bytes anderror bytes in the first occurrence of the outbound message, determiningcorrect bytes and error bytes in the second occurrence of the outboundmessage, and assembling a reconstructed outbound message at the one ofthe plurality of remote powered vehicles using correct bytes from thefirst or the second occurrence of the outbound message.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more easily understood and the furtheradvantages and uses thereof more readily apparent, when considered inview of the following detailed description when read in conjunction withthe following figures, wherein:

FIGS. 1 and 2 are schematic illustrations of a distributed power trainto which the teachings of the present invention can be applied.

FIG. 3 is a timing diagram of a prior art normal message priorityprotocol for a communications system.

FIG. 4 is a timing diagram of an onboard message priority protocol,according to the teachings of the present invention, for use with atrain comprising four remote units.

FIG. 5 is a table illustrating timing parameters for the onboard messagepriority protocol according to the teachings of the present invention.

FIG. 6 is a timing diagram of another embodiment of an onboard messagepriority protocol, according to the teachings of the invention, for usewith a train comprising four remote units.

FIG. 7 is a timing diagram of an onboard message priority protocol,according to the teachings of the present invention, for use with atrain comprising three remote units.

FIG. 8 is a timing diagram for an off-board message repeater systemaccording to the teachings of the present invention.

FIG. 9 is a table illustrating timing parameter comparisons for thenormal priority message protocol, the onboard repeater message priorityprotocol and the off-board repeater message priority protocol.

FIG. 10 is a schematic illustration of a distributed power trainaccording to another embodiment of the present invention.

FIGS. 11 and 12 are flowcharts depicting processing steps according totwo embodiments of the present invention.

In accordance with common practice, the various described features arenot drawn to scale, but are drawn to emphasize specific featuresrelevant to the invention. Reference characters denote like elementsthroughout the figures and text.

DETAILED DESCRIPTION OF THE INVENTION

Before describing in detail the particular method and apparatus for apriority message protocol for an on-board message repeater system inaccordance with the present invention, it should be observed that thepresent invention resides primarily in a novel combination of hardwareand software elements related to said method and apparatus. Accordingly,the hardware and software elements have been represented by conventionalelements in the drawings, showing only those specific details that arepertinent to the present invention, so as not to obscure the disclosurewith structural details that will be readily apparent to those skilledin the art having the benefit of the description herein.

According to a preferred embodiment of the present invention, comprisinga priority message protocol for an on-board message repeater system in adistributed power train, such as the distributed power train 10 of FIG.1, messages transmitted from the lead unit 14 leapfrog down the trainfrom the head end to the end-of-train as each successive remote unit12A-12C receives and retransmits the message.

Further, when the train enters an environment where the lead locomotiveunit may not successfully communicate directly with each remote unit(for example, when the train enters a tunnel), the communications systemmay automatically switch to the priority protocol for on-board messagerepeating (OBMR) according to the teachings of the present invention.Such a switch occurs, for example, when the communications systemexperiences an interrupt of more than a predetermined fixed duration,one minute for example. Once activated, in one embodiment the OBMRprotocol is active for fifteen minutes, after which the communicationssystem returns to normal priority message protocol operation, i.e., asdescribed in conjunction with FIG. 3. In another embodiment, thecommunications system can be configured for continual OBMR operation orOBMR operation can be manually activated by the lead locomotiveoperator.

FIG. 4 illustrates an exemplary OBMR protocol for a train comprising alead unit and four remote units. In this mode, the lead unit transmits acommand message (i.e., a message that commands a new function at theremote units or a status update message that requests remote unit statusinformation and also includes the most recent previously-transmittedcommand). The first remote unit receives the outbound command messageand repeats the message for receiving by other remote units in thetrain.

As illustrated in FIG. 4, the lead unit transmission begins at 625 msecafter a time t=0. This interval is merely exemplary and represents apredetermined minimum interval between receipt of a message at the leadunit and a transmission of a later command from the lead unit. Note theexemplary 50 msec delay interval between the end of a messagetransmission and retransmission of the message, and also the allottedexemplary 30 msec radio (transceiver) turn-on time. Generally, thecommand messages sent by the lead unit, the messages sent by the remoteunits and the interval between message transmissions are fixed inlength. However, these lengths may vary as needed for a particularapplication of the present invention and may differ among differentrailroad operators.

Unlike the normal communications mode described above, according to oneembodiment of the invention the first remote does not transmit a returnstatus message upon receipt of the outbound message that was sent fromthen lead locomotive. Instead, the first remote unit (and eachsubsequent remote unit) repeats the outbound message, thereby permittingthe outbound message to propagate along the length of the train, withoutincurring the time penalty of the inbound (i.e., in a direction towardthe lead locomotive) status messages transmissions from each remoteunit. As can be seen from FIG. 4, each remote unit retransmits theoutbound message within its respective predefined time slot, apredetermined time interval after receiving the outbound message, afteranother remote unit has transmitted the transmitted the outboundmessage, or after another remote unit has transmitted a response. Thusthe message leapfrogs down the train for receiving by each remote unit.When the outbound message is retransmitted by the last remote, no statusmessages have been returned to the lead locomotive.

One premise of certain embodiments of the invention is that eachlocomotive of the train receives (e.g., “hears”) messages sent from thelead locomotive and from the remote locomotive(s), although this may notalways be true due to interference, low signal strength, etc. The signaltiming parameters and actions at the lead and remote units as describedherein are based on this premise. If a remote unit fails to receive alead message, for example, this situation is discovered when the leadunit fails to receive a response from that remote locomotive. The leadlocomotive takes corrective action, including retransmitting theoriginal message.

Also, it can be seen from FIG. 4 that each remote locomotive waits apredetermined time from receiving the message (either from receiving theoutbound message or from receiving the inbound message) from the leadlocomotive or from a prior remote locomotive, where “prior” refers to alocomotive that received the message earlier in time and transmits aresponse message or retransmits the received message. However, if theprior remote locomotive did not receive the message, it obviously cannottransmit a response message or retransmit the original message. Underthese circumstances a remote locomotive expecting a response from theprior locomotive will not receive that response. The remote locomotiveexpecting the response will therefore wait a predetermined time fromreceipt of the last message until sending its own message orretransmitting the original message.

When setting up the communications system as described above, eachlocomotive is configured to reflect its position in the train. Thus eachmessage sent by a locomotive includes an identifier of the transmittinglocomotive. Each locomotive receiving the message can thereforedetermine the locomotive that transmitted the message and can alsodetermine the position of the transmitting locomotive in the trainrelative to the position of the receiving locomotive.

When the last remote (the nth remote) receives the command message, thelast remote sends its status message (i.e., an inbound message) back tothe previous (n-1)th remote. According to standard practice, when thecommunications system is configured or the lead and remote units arelinked, the remote unit farthest from the lead unit is configured as thelast remote, i.e., the last remote “knows” that it is the last remote inthe train. Thus when the last remote unit receives the outbound messageit responds with its status message. Remote unit three (in the casewhere n=4) receives the status message from remote unit four and storesthe received status message until its designated time slot, at whichtime remote unit three repeats the remote unit four status message andappends its own status message, transmitting both status messages in adirection of the lead unit, i.e., to the second remote. Remote unit tworeceives the status messages from remote units four and three, andtransmits these status messages, plus its own status message, in thedirection of the lead unit. The process continues until each remoteunit's status message reaches the lead unit as a concatenated messagecomprising the status message from each remote unit.

As can be seen from FIG. 4, this occurs at t=4377 msec, or a totalelapsed time of 3752 msec from the start of transmission of the outboundcommand message to receipt of all status messages at the lead unit.

According to standard operation procedure of the distributed power traincommunications system, in the event that a remote unit did not receivethe outbound message as it was originally transmitted from the lead unitor as the message was successively repeated by the remote units, anon-receiving remote unit will not have a status message to report backto the lead unit. The lead unit expects a status message from each ofthe remote units and can determine from the received status messages(each remote unit status message includes a remote unit identifier)which if any of the remote units did not receive the command message.Thus if the lead unit does not receive a status message from one or moreremotes, the command is retransmitted by the lead unit. According to oneembodiment, the lead operator is informed of this remote unit miss by anappropriate indication on a lead unit display.

As can be appreciated by those skilled in the art, a status messagetransmitted by a remote unit may be received by remote units in additionto the intended receiving remote unit, i.e., where the intendedreceiving remote unit is that remote unit adjacent to the transmittingremote unit in a direction toward the lead unit of the train. Forexample, in the FIG. 4 distributed power train having four remote units,both remote units two and three may receive the status messagetransmitted by the remote unit four. Remote unit two stores the remotefour status message until its designated transmitting time slot or untila designated time interval from receipt of the message from the lastremote to transmit the message. Thus remote unit two may receive theremote four status message twice: (1) when initially transmitted by theremote unit four, and (2) when retransmitted by remote unit three. Thecapability of multiple receptions of a status message improves theprobability that the lead unit receives the status message from eachremote unit that received the command message.

In one embodiment, a remote unit receiving the message twice, asdescribed immediately above, compares the two messages, byte by byte.Each byte of the message includes an error detection code (for example,a parity check), thus permitting a determination that each byte iserror-free (the parity check indicated that no errors had occurred) orcontains errors (the parity check indicated that at least one erroroccurred). If a byte in a first message failed the parity check and thesame byte in a second message passed the parity check, then the failedbyte in the first message is replaced by the correct byte from thesecond message.

In another embodiment, a message is received at both antennas 29A and29B and processed through associated transceivers 28A and 28B of any ofthe remote locomotives 15, 12A, 12B and 12C and the lead locomotive 14.See FIG. 1. Both messages are the processed through the lead station 30or the remote station 32, as appropriate, where the two messages arecompared byte by byte. Each byte of each message includes an errordetection code (for example, a parity check), thus permitting adetermination that a byte is error-free (the parity check indicatingthat no errors were present) or a byte contains at least one error (theparity check indicating that at least one error is present). If a bytein a first message failed the parity check and the same byte in a secondmessage passed the parity check, then the failed byte in the firstmessage is replaced by the correct byte from the second message toassemble a corrected message. The corrected message is then processedthrough the associated lead station 30 or the remote station 32.

FIG. 5 is a table indicating the relative transmission order, delaytime, and message content for the message priority protocol for on-boardmessage repeating for a train comprising one lead locomotive and fourremote locomotives as illustrated in FIG. 4. However, when a remote unittransmits, the time delay period from the third column of FIG. 5 foreach later-transmitting remote is decremented as explained below.

The time delay between the end of a transmission from one unit and thebeginning of a transmission from another unit is 50 msec in theillustrated embodiment. As each remote unit transmits, the time delayfor each subsequent remote to transmit is reduced by 50 msec thusallowing each remote unit to transmit in order while maintaining 50 msecbetween each unit's transmission. If a remote unit does not transmitafter its defined time delay then each subsequent remote recognizes thisand adjusts its own time delay accordingly when a subsequent unit'stransmission is received.

For example, if remote unit one does not transmit, remote unit two waits100 msec from the end of the lead unit transmission before it transmits.If remote unit two transmits, then each subsequently transmitting remoteunit recognizes that two remotes should have transmitted in this timeframe and subtracts 100 msec from its time delay; remote unit threetransmits 50 msec (150-100 msec) after the end of the remote unit twotransmission, with remote four transmit delay adjusted to 100 msec(200-100 msec) after the end of the remote unit two transmission, etc.

But if remote unit two does not transmit (and remote unit one did nottransmit) then remote unit three is set to transmit 150 msec after theend of the lead unit transmission and when remote unit three transmitseach subsequently transmitting remote unit recognizes that three remoteunits should have transmitted in this time frame and each subtracts 150msec from its time delay.

Finally, if the remote units one, two and three do not transmit, thenremote unit four waits 200 msec from the end of the lead unittransmission to transmit and when remote four transmits eachsubsequently transmitting remote unit will recognize that four remoteunits should have transmitted in this time frame and each thereforesubtracts 200 msec from its time delay.

In another example, if the lead unit and the first remote unit transmit,then the second remote unit transmits at 100−50=50 msec from the end ofthe first remote transmission. The third and fourth remote units alsosubtract 50 msec from their delay period and they are set to transmit at100 msec and 150 msec, respectively, from the end of the first remotetransmission if remote unit two does not transmit.

When the second remote units transmits 50 msec after the end of thefirst remote transmission, then all subsequent remotes subtract 50 msecfrom their previously adjusted time delay (i.e., the previous adjustmentof subtracting 50 msec due to the transmission of remote unit one) andthe third remote unit transmits at 100−50=50 msec. from the end of thesecond remote transmission. The fourth remote unit also subtract 50 msecfrom its previously adjusted delay and is set to transmit at 150−50msec=100 msec, from the end of the second remote transmission if remoteunit three does not transmit. When the third remote units transmits 50msec after the end of the second remote transmission, then allsubsequent remotes again subtract 50 msec from their previously adjustedtime delay and the fourth remote unit transmits at 100−50=50 msec fromthe end of the third remote transmission,

Generally, as each remote unit transmits and the message is received byall other remote units, then each remote unit that has not yettransmitted the message subtracts 50 msec from its assigned time delayperiod. This shortening of the time delay period reduces the timerequired for the message to leap frog up and down the train.

Consider a scenario where one or more remote units do not transmit. Forexample assume the lead unit transmits a command message and 50 msecafter the command message ends remote unit one transmits the commandmessage. At this point each remote unit has heard the transmission fromremote unit one and therefore has subtracted 50 msec from its assignedtime delay. Assume further that remote unit two did not transmit 50 msecafter remote unit one ended its transmission. Remote unit three hastherefore reduced its time delay to 150−50=100 msec, where the 50 msecreduction is due to the transmission by remote unit one. Remote unitthree will transmit 100 msec after the end of the last transmission,which in this case is the transmission from remote unit one.

Assume instead that remote unit one did not transmit the message fromthe lead unit and remote unit two did not transmit the message. Remoteunit three therefor transmits at 150 msec from the end of the lead unittransmission. Remote unit four subtracts 150 msec (due to recognizingthat remote 1, 2 and 3 should have transmitted in this time frame) fromits assigned time delay; 200−150=50 msec. Remote unit four will transmit50 msec after the end of the remote unit three transmission.

As can be seen, the 50 msec interval is a sliding interval, such thatwhenever a remote unit transmits a signal, the next remote waits 50 msecfrom the end of the transmission before initiating its transmission. Ifa remote unit does not transmit a signal then the subsequent remoteunits wait their assigned time delay period less 50 msec for each remoteunit that transmitted or should have transmitted the signal.

According to a variant of the OBMR protocol described in conjunctionwith FIGS. 4 and 5, during the period when status messages aretransmitted by the remote units in the direction of the lead unit, theoutbound command message is also transmitted by the remote units tomaximize the opportunity for each remote unit to receive the commandmessage. This scenario, which is illustrated in FIG. 6, extends the timebetween transmission of the command message from the lead unit andreceipt of the remote status messages at the lead unit, with the benefitof increasing the probability that each remote unit receives theoutbound message.

FIG. 7 is a timing diagram for the message priority protocol foron-board message repeater for a train comprising a lead locomotive andthree remote locomotives. The implementation principles for adistributed power train comprising three remote units are identical tothe implementation for a four remote unit distributed power train asdescribed above in conjunction with FIG. 4. As can be appreciated bythose skilled in the art, the embodiment illustrated in FIG. 6 whereinthe remote units retransmit the command message can also be applied to atrain comprising a lead unit and three remote locomotives (or a traincomprising any number of remote units).

FIG. 8 is a timing diagram for the normal communications timing protocolwhen operative with the off-board message repeater 26 described above inconjunction with FIG. 1. The lead unit transmits a command messageduring time interval 200 that is received and retransmitted by themessage repeater 26 during time interval 202. Each of four remote unitsreceives the repeated command message and responds with its statusmessage during its allotted time slot. The repeater 26 receives all theremote unit status messages and retransmits them for receiving by thelead unit 14 during time interval 206, after which the message intervalends.

A utility message 210 referenced in FIG. 8 is a message sent by therepeater 26 to all lead units in radio range of the repeater 26, causingall receiving lead units to delay transmissions. For example, theutility message prevents a lead unit that is outside of a tunnel fromtransmitting simultaneously with a remote unit that is inside thetunnel.

FIG. 9 compares message delay times of the prior art normal messageprotocol, the OBMR protocol of the present invention, and the normalmessage timing protocol when operative with the off-board messagerepeater.

In other embodiments, the communications system of the present inventionfurther comprises an antenna/radio diversity feature and/or a signalselection feature that are advantageous to overcome signal transmissionpath impairments such as caused by multi-path signal propagation, signalreflections and signal obstructions (such as due to a locomotive-mountedpantograph for supplying electrical power to the locomotive fromoverhead power cables).

Each consist of two locomotives comprises a forward locomotive250A/250B/250C and a rearward locomotive 252A/252B/252C (see FIG. 10),each locomotive further comprising a forward radio 260A/260B/260C and arearward radio 262A/262B/262C, each forward radio operative inconjunction with an antenna 266A/266B/266C and each rearward radiooperative in conjunction with an antenna 268A/268B/268C, respectivelyfor receiving messages sent from other locomotives of a train 270. Theconsist locomotives are coupled by an MU (multiple unit) cable253A/253B/253C. According to conventional railroad parlance, the forwardlocomotive 250A/250B/250C is designated the “A” unit controlling thelocomotive 252A/252B/252C or “B” unit by control signals initiated bythe train operator in the “A” unit and supplied to the “B” unit over theMU cable 253A/253B/253C.

It is noted that the concepts described herein also apply to a singlelocomotive comprising two radios and associated two antennas, onelocated at each end of the locomotive, with a pantograph or anotherobstruction located between the two antennas.

When the communications system is activated, the forward radios260A/260B/260C and the rearward radios 262A/262B/262C in each locomotiveconsist are activated. Thus both radios in each consist receive messagestransmitted by other units in the train 270. Both the forward radios260A/260B/260C and the rearward radios 262A/262B/262C determine a signalquality metric (such as the signal strength, bit error rate, or thereception of valid data) for each received message. The signal qualitymetrics are compared in a comparator/processor 276A/276B/276C, and themessage having the better signal quality metric is selected as theoperative message for use by the locomotives consist.

According to a preferred embodiment, the signal quality metric isdetermined for all messages received at the forward radios260A/260B/260C and the rearward radios 262A/262B/262C to select theoperative message for that consist. For example, each received radiomessage can be verified to be correct by subjecting the message to anerror detection and correction algorithm, followed by processingaccording to the present invention to determine the signal qualitymetric of the signal received at each radio of the consist, from whichthe operative message for the consist is selected.

Alternatively, in lieu of processing the entire signal for determiningthe signal quality metric, only a first group of message bits areanalyzed to determine the signal quality metric of the message. Themessage with the better signal quality metric is selected as theoperative message for the consist.

Typically, outbound messages are transmitted from the antenna/radio268A/262A of the lead consist and status messages are transmitted fromthe antennas/radios 266B/260B and 266C/260C of the remote consists. Inyet another embodiment, to minimize interference that can disruptaccurate reception of received signals, one of the antennas266A/266B/266C (and the corresponding radio 260A/20B/260C) or one of theantenna 268A/268B/268C (and the corresponding radio 262A/262B/262C) isselected as the transmitting antenna in response to a desired directionfor the transmitted signal. Note that the antennas 266A/266B/266C aredisposed proximate a forward end of the associated locomotive consist(assuming a direction of travel indicated by the arrowhead 11) and theantennas 268A/268B/268C are disposed at a rearward end of the associatedlocomotive consist.

The radio 260A/260B/260C/262A/262B/262C determines an intended directionfor the transmitted signal (e.g., inbound or outbound based on the typeof signal and/or information contained in the signal) and selects thetransmitting antenna/radio that is closest to the intended receivingantenna/radio. For example, if the locomotive consist comprising thelocomotives 250A and 252A is the lead consist and it is desired totransmit an outbound message to the locomotive consist comprising thelocomotives 250B and 252B, then the antenna/radio 268A/262A is selectedas the operative antenna. This feature can be especially beneficial wheneach locomotive comprises a pantograph 280 for supplying current to thelocomotives from an overhead current source (not shown in FIG. 10).According to this embodiment, an antenna (and corresponding radio) isselected such that the desired signal direction is away from thepantograph. As a further example, if the remote locomotive consistcomprising the locomotives 250B and 252B is to send a signal to thelocomotive consist comprising the locomotives 250A and 252A, then theantenna/radio 266B/260B is selected as the operative antenna/radio.

FIG. 11 is a flow chart illustrating the method for implementing thesignal selection function according to one embodiment of the presentinvention. In one embodiment, the FIG. 11 method is implemented in amicroprocessor and associated memory elements within the locomotives ofthe railroad train, for example, within the locomotives260A/260B/260C/262A/262B/262C. In such an embodiment the FIG. 11 stepsrepresent a program stored in the memory element and operable in themicroprocessor. When implemented in a microprocessor, program codeconfigures the microprocessor to create logical and arithmeticoperations to process the flow chart steps. The invention may also beembodied in the form of computer program code written in any of theknown computer languages containing instructions embodied in tangiblemedia such as floppy diskettes, CD-ROM's, hard drives, DVD's, removablemedia or any other computer-readable storage medium. When the programcode is loaded into and executed by a general purpose or a specialpurpose computer controlled by a microprocessor, the computer becomes anapparatus for practicing the invention. The invention can also beembodied in the form of a computer program code, for example, whetherstored in a storage medium loaded into and/or executed by a computer ortransmitted over a transmission medium, such as over electrical wiringor cabling, through fiber optics, or via electro-magnetic radiation,wherein when the computer program code is loaded into and executed by acomputer, the computer becomes an apparatus for practicing theinvention.

The FIG. 11 flow chart begins at a step 300 where the communicationssystem is activated, thus the forward radios (260A/260B/260C in FIG. 10)and the rearward radios (262A/262B/262C in FIG. 10) in each locomotiveconsist are activated. As indicated at a step 302, both radios in eachconsist receive messages transmitted by other units in the train 270. Asindicated at a step 304, both the forward radios and the rearward radiosdetermine a signal quality metric (such as the signal strength, biterror rate, or the reception of valid data) for each received message.The signal quality metrics are compared at a step 306 and the messagehaving the better signal quality metric is selected (see a step 310) asthe operative message for use by the locomotive consist.

A flowchart of FIG. 12 depicts the antenna/radio diversity feature ofone embodiment of the present invention. At a step 330 a signal isproduced for transmitting to another locomotive in the train. At a step332 an intended direction for the transmitted signal (e.g., inbound oroutbound based on the type of signal and/or information contained of thesignal) is determined. At a step 334, the transmitting antenna/radio isselected as the antenna/radio that is closest to the intended receivingantenna/radio.

Certain embodiments herein have been described with respect to railroadtrains. Any of such embodiments, unless otherwise specified (such as inthe claims), are also applicable to rail vehicle consists or othervehicle consists more generally, a “vehicle consist” referring to agroup of linked vehicles that travel together along a route. Forexample, a “rail vehicle consist” is a group of linked vehicles thattravel together along a set of rails or other guideway. As anotherexample, a “marine vehicle consist” is a group of marine vessels linkedtogether to travel along a waterway. Additionally, other embodimentsherein have been described with respect to locomotives. Any of suchembodiments, unless otherwise specified (such as in the claims), arealso applicable to powered rail vehicles or other powered vehicles moregenerally. A “powered vehicle” is a vehicle (marine, on-road, off-road,etc.) capable of self-propulsion. A “powered rail vehicle” is a vehicleconfigured for self-propulsion along a pair of rails or other guideway.

While the invention has been described with reference to preferredembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalent elements may be substitutedfor elements thereof without departing from the scope of the presentinvention. The scope of the present invention further includes anycombination of the elements from the various embodiments set forthherein. In addition, modifications may be made to adapt a particularsituation to the teachings of the present invention without departingfrom its essential scope. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. A communications method for a vehicle consist comprising a leadpowered vehicle having a first antenna associated with a firsttransceiver and a second antenna associated with a second transceiverand a remote powered vehicle having a third antenna associated with athird transceiver and a fourth antenna associated with a fourthtransceiver, the method comprising: transmitting an outbound messagefrom the first transceiver via the first antenna or from the secondtransceiver via the second antenna, the outbound message comprising aplurality of message bytes; receiving the outbound message at the thirdand the fourth antennas and the associated third and fourthtransceivers; determining correct bytes and error bytes in the outboundmessage as received at the third transceiver; determining correct bytesand error bytes in the outbound message as received at the fourthtransceiver; and assembling a reconstructed message using correct bytesfrom one of the message received at the third transceiver and themessage received at the fourth transceiver.
 2. The communications methodof claim 1 wherein each message byte comprises a data portion and anerror detection portion.
 3. The communications method of claim 2 whereinthe error detection portion comprises a parity check portion.
 4. Thecommunications method of claim 1 further comprising transmitting aninbound message from the third transceiver via the third antenna or fromthe fourth transceiver via the fourth antenna, the inbound messagecomprising a plurality of message bytes; receiving the inbound messageat the first and the second antennas and the associated first and secondtransceivers; determining correct bytes and error bytes in the inboundmessage as received at the first transceiver; determining correct bytesand error bytes in the inbound message as received at the secondtransceiver; and at the lead powered vehicle assembling a reconstructedmessage using correct bytes from one of the message received at thefirst transceiver and the message received at the second transceiver. 5.A communications method for a vehicle consist comprising a lead poweredvehicle and a plurality of remote powered vehicles, the methodcomprising: transmitting an outbound message from the lead poweredvehicle, the outbound message comprising a plurality of message bytes;one or more of the plurality of remote powered vehicles receiving andretransmitting the outbound message; receiving a first occurrence of theoutbound message at a one of the plurality of remote powered vehicles;receiving a second occurrence of the outbound message at the one of theplurality of remote powered vehicles; determining correct bytes anderror bytes in the first occurrence of the outbound message; determiningcorrect bytes and error bytes in the second occurrence of the outboundmessage; and assembling a reconstructed outbound message at the one ofthe plurality of remote powered vehicles using correct bytes from thefirst or the second occurrence of the outbound message.
 6. Thecommunications method of claim 5 wherein each message byte comprises adata portion and an error detection portion.
 7. The communicationsmethod of claim 6 wherein the error detection portion comprises a paritycheck portion.
 8. The communications method of claim 5 furthercomprising: transmitting an inbound message from a one of the pluralityof remote powered vehicles, the inbound message comprising a pluralityof message bytes; other ones of the plurality of remote powered vehiclesreceiving and retransmitting the inbound message; receiving a firstoccurrence of the inbound message at a one of the plurality of remotepowered vehicles or at the lead powered vehicle; receiving a secondoccurrence of the inbound message at the one of the plurality of remotepowered vehicles or at the lead powered vehicle; determining correctbytes and error bytes in the first occurrence of the inbound message;determining correct bytes and error bytes in the second occurrence ofthe inbound message; and assembling a reconstructed inbound message atthe one of the plurality of remote powered vehicles or at the leadpowered vehicle using correct bytes from the first or the secondoccurrence of the outbound message.
 9. The communications method ofclaim 8 wherein each message byte comprises a data portion and an errordetection portion.
 10. The communications method of claim 9 wherein theerror detection portion comprises a parity check portion.
 11. Acommunications method for a vehicle consist comprising a lead poweredvehicle consist comprising a forward powered vehicle having a firstantenna associated with a first transceiver and a rearward poweredvehicle comprising a second antenna associated with a secondtransceiver, the vehicle consist further comprising a remote poweredvehicle consist comprising a forward powered vehicle having a thirdantenna associated with a third transceiver and a rearward poweredvehicle comprising a fourth antenna associated with a fourthtransceiver, the method comprising: transmitting an outbound messagefrom the first transceiver via the first antenna or from the secondtransceiver via the second antenna, the outbound message comprising aplurality of message bytes; receiving the outbound message at the thirdand the fourth antennas and the associated third and fourthtransceivers; determining correct bytes and error bytes in the outboundmessage as received at the third transceiver; determining correct bytesand error bytes in the outbound message as received at the fourthtransceiver; and assembling a reconstructed message using correct bytesfrom one of the message received at the third transceiver and themessage received at the fourth transceiver.
 12. The communicationsmethod of claim 11 wherein each message byte comprises a data portionand an error detection portion.
 13. The communications method of claim12 wherein the error detection portion comprises a parity check portion.14. The communications method of claim 11 further comprising:transmitting an inbound message from the third transceiver via the thirdantenna or from the fourth transceiver via the fourth antenna, theinbound message comprising a plurality of message bytes; receiving theinbound message at the first and the second antennas and the associatedfirst and second transceivers; determining correct bytes and error bytesin the inbound message as received at the first transceiver; determiningcorrect bytes and error bytes in the inbound message as received at thesecond transceiver; and assembling a reconstructed message using correctbytes from one of the message received at the first transceiver and themessage received at the second transceiver.